1. Field of the Invention
The present invention relates to a method of generating image data, and more particularly, to a method of generating image data including intra prediction for determining a prediction mode with ease.
2. Description of the Background Art
As the latest international standard for moving picture encoding, the Video Coding Experts Group (VCEG) of the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) and the Moving Picture Experts Group (MPEG) of ISO/IEC, which are international organizations for standardization dealing with telecommunication, have developed H.264 to be put to practical use.
H.264 is capable of performing compression twice volume as much as MPEG-2 and MPEG-4 while maintaining the same level of image quality, and thus is applicable to a wide range of use from a low bit-rate teleconference to a high definition television (HDTV).
One of the characteristics of H.264 is a mode referred to as intra-frame prediction (intra prediction). This is a mode for improving a compressibility with the use of pixel correlation, in which a prediction image is generated through interpolation of data between subblocks, and encoded subblocks adjacent to an encoding target subblock are referred to, to thereby perform prediction by comparison at a pixel level.
Intra prediction is adopted also in MPEG-4, in which left, upper and upper-left subblocks are referred to. On the other hand, left, upper, upper-left and upper-right subblocks are referred to in H.264, whereby a prediction image with a higher degree of accuracy is obtained.
Prediction is performed in 8 by 8 pixels in MPEG-4, whereas in H.264, a complicated image is predicted in 4 by 4 pixels, and a simple image is predicted in 8 by 8 pixels and 16 by 16 pixels, which enables efficient prediction.
In H.264 intra prediction as described above, an optimum prediction mode is determined by four patterns of prediction methods (prediction modes) in a case of prediction in 16 by 16 pixels, and by nine patterns of prediction modes in cases of prediction in 8 by 8 pixels and prediction in 4 by 4 pixels, which requires an enormous amount of computing, leading to a problem that it takes long time before prediction results are obtained.
Japanese Patent Application Laid-Open No. 2007-282014 discloses the technology of using simplified intra prediction in which a pixel value prior to encoding is also used as a prediction value for performing intra prediction and normal intra prediction in combination, so that high efficiency is achieved in intra prediction to reduce time required for intra prediction. However, much higher efficiency is required as a display apparatus becomes larger.